Battery types

The high-antimony battery (antimony levels of about 6-7%) has good durability against vibration, but has a great water drainage. Applications include lift forks etc.
The low-antimony battery (1-2% antimony) is “almost” maintenance-free, slightly more sensitive to vibrations and is suitable for e.g. recreational use.
At the correct charge, the calcium battery (2-3%) has no water loss and is often completely closed (no openable plugs to add water). Good cold start properties and suitable for automotive use.
Not suitable in applications where deep discharge can occur.

Gel and AGM

In addition to the mechanical structure (flat or tube cell) and the addition of different hardening chemistry, the acid content may also be in different states.
Batteries with openable plugs (to add water) have free liquid (sulphuric acid + distilled water).

The liquid may instead be in gel form (GEL) or absorbed in a glass fibre floss (AGM) in some battery types.
No water can be supplied because the battery has no plugs. On the other hand, there are safety valves that open at excessive pressure in the cell (usually due to incorrect charging). The battery types are often used in environment with no special drawer cabinets or other powerful exhaust ventilation (office, wheelchair etc.). The battery can be mounted in any position (lying / standing). Another advantage is that if the plastic container is damaged, no acid flows out.
This group of batteries is often called VRLA (valve-regulated lead-acid battery).

What happens when a battery is discharged and recharged?